Mercenaries are characterized primarily by their high skill and speed, with their other stats (excluding magic and resistance) being decent. From The Binding Blade onward, mercenaries have a counterpart in the myrmidon, which has even higher speed and skill, but lower strength and defense.

The term "mercenary" can refer to a unit of this class, but it also can refer to one who fights and kills for pay. For example, Raven of Fire Emblem: The Blazing Blade is a mercenary unit, but does not fight for pay. However, Gerik of The Sacred Stones is a mercenary unit and also fights for pay, along with Marisa, who is a myrmidon.

Mercenaries are strong fighters, making them popular units. Their high HP and attack make them useful units who can be put in the front lines with little danger.